A conventional turbocharger typically relies on a center housing rotating assembly (CHRA) that includes a turbine wheel and a compressor wheel attached to a shaft rotatably supported by a bearing assembly located in a bore of a center housing. A typical bearing assembly or bearing cartridge includes an outer race and an inner race, configured to receive a shaft, where the outer race and the inner race are separated by rolling elements such as ball bearings.
In most CHRAs, a so-called “locating mechanism” restricts movement of a bearing assembly in the bore of the center housing. Various conventional locating mechanisms rely on radial insertion of a locating pin in an opening of an outer race of a bearing assembly. Such a mechanism restricts radial and/or axial movement of the bearing assembly and rotation of the outer race yet allows the inner race to spin freely. Additionally, such a mechanism allows for some radial movement of a bearing assembly, usually within defined clearances that fill with lubricant during operation to form a “squeeze film” that acts to damp vibration and noise. In such a CHRA, the degrees of radial and axial freedom may be chosen to be of particular magnitude or magnitudes depending on various goals.
Various issues can arise with locating mechanisms that rely on a radial locating pin to locate a bearing assembly. For example, during operation of a turbocharger, significant axial loads can be generated that thrust the turbocharger shaft and associated components toward the compressor end or toward the turbine end of the turbocharger CHRA, which, in turn, can be transferred from the bearing assembly to the radial locating pin. Such forces make pin strength an important design factor. Another issue pertains to axial stack-up of components (e.g., how well do the components of a CHRA stack and how does this stacking affect operation and wear). In general, a locating mechanism that relies on a radial locating pin does not provide advantages with respect to axial stacking; indeed, the nature of the pin and the outer race opening introduce geometric and operation concerns that can be disadvantageous.
More generally, a locating mechanism, such as the aforementioned radial pin locating mechanism, can be described in terms of “key/keyway pairs” that involve male (key) and female (keyway) components that act to locate an outer race of a bearing assembly. In such key/keyway-based locating mechanisms, frictional contact between key and keyway components should remain low (1) to allow a bearing assembly to move freely in the radial plane (i.e., within its squeeze film) and (2) to limit wear between the keyway components.
Additionally, in a CHRA, to maximize efficiency and reduce powerloss, frictional contact between components should be minimized. For turbochargers, the one source of powerloss stems from the bearing system. As described herein, various exemplary locating mechanisms can reduce or alleviate issues associated with locating mechanisms that rely on radial pins. For example, by reducing friction, such exemplary mechanisms can reduce powerloss and thereby improve efficiency and performance of turbocharged internal combustion engines.